The present invention relates to a method and a device for safeguarding a hazardous area, in particular the hazardous area of an automatically operating machine. In more detail, the invention relates to such a method and such a device using at least a first and a second image recording unit for recording at least two images of the hazardous area.
Hazardous areas, in particular hazardous areas of machines and industrial plants, are usually safeguarded so far by using light barriers, light curtains or laser scanners, often in combination with additional mechanical barriers. However, such protective measures require complicated installation and adjustment. In addition, these protective measures are not very flexible when it is desired to adapt the safeguarding of the hazardous area to different operational situations.
In order to overcome these disadvantages, attempts have been made for some time to safeguard a hazardous area by means of an image recording unit, typically a digital camera, and by means of intelligent image evaluation methods. Reference is made in this regard to DE 199 38 639 A1, by way of example. This reference discloses a device for safeguarding a hazardous area wherein a virtual barrier is generated in front of the hazardous area by means of the image recording unit and by means of an artificial, “cooperative” target. Breaking through the barrier can be detected with the image recording unit in the same way as in the case of a light barrier. If appropriate, the machine from which the hazard originates is switched off thereupon or put into a non-hazardous state in some other way.
Although this known device is already substantially easier to install and exhibits a higher level of flexibility than conventional light barriers etc., it is still a disadvantage that installation measures are required with the “cooperative target” in the area of the machine to be safe guarded.
A device having two image recording units arranged at a spacing from one another is disclosed by DE 197 09 799 A1. The images, which are supplied to an evaluation unit from the two image recording units, are subjected to a stereo image analysis in order to obtain a three-dimensional image of the hazardous area. The three-dimensional image is subsequently compared with a three-dimensional reference model in order to detect foreign objects, i.e. objects located inadmissibly in the hazardous area. However, it has emerged from practical experiments with a comparable arrangement that the reliability of detection with which the foreign objects can be detected in the hazardous area is inadequate. This applies at least to the extent that such a device is to be used for protecting persons from automatically operating machines. Extremely short reaction times (in the range of 30 ms) and a virtually one hundred percent reliability of detection are required for such an application.
A similar device and a corresponding method are also disclosed by EP 1 061 487 A1, and what has been said above with regard to the disadvantages also applies here.
DE 198 09 210 A1 discloses a device and a method for monitoring what is called a scene. The scene is recorded with a single image recording unit and compared with a reference image. Individual points inside the scene are specifically illuminated by means of a light source in order to obtain a marking or individualization when recording the image. However, this method has the disadvantage that the illumination of the scene, thus of the hazardous area in the specific case of application, causes susceptibility to faults owing to the incursion of scattered extraneous light. Faults owing to extraneous light can occur, in particular, in industrial production environments, for example with welding robots or with large brake presses.